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Using SCTP to Improve QoS and Network Fault-Tolerance of DRE Systems

Using SCTP to Improve QoS and Network Fault-Tolerance of DRE Systems. OOMWorks LLC BBN Technologies LM ATL Metuchen, NJ Cambridge, MA Camden, NJ Yamuna Krishnamurthy Craig Rodrigues Gautam Thaker

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Using SCTP to Improve QoS and Network Fault-Tolerance of DRE Systems

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  1. Using SCTP to Improve QoS and Network Fault-Tolerance of DRE Systems OOMWorks LLC BBN Technologies LM ATL Metuchen, NJ Cambridge, MA Camden, NJ Yamuna Krishnamurthy Craig Rodrigues Gautam Thaker Irfan Pyarali Prakash Manghwani Real-Time and Embedded Systems Workshop • July 12-15, 2004 • Reston, Virginia, USA

  2. Transport Protocol Woes in DRE Systems

  3. Stream Control Transport Protocol (SCTP) • IP based transport protocol originally designed for telephony signaling • SCTP supports features found to be useful in TCP or UDP • Reliable data transfer (TCP) • Congestion control (TCP) • Message boundary conservation (UDP) • Path MTU discovery and message fragmentation (TCP) • Ordered (TCP) and unordered (UDP) data delivery • Additional features in SCTP • Multi-streaming: multiple independent data flows within one association • Multi-homed: single association runs across multiple network paths • Security and authentication: checksum, tagging and a security cookie mechanism to prevent SYN-flood attacks • Multiple types of service • SOCK_SEQPACKET – message oriented, reliable, ordered/unordered • SOCK_STREAM – TCP like byte oriented, reliable, ordered • SOCK_RDM – UDP like message oriented, reliable, unordered • Control over key parameters like retransmission timeout and number of retransmissions

  4. Integration of SCTP in DRE Systems • Issues with integrating SCTP directly • Possible re-design of the system • Accidental and Incidental errors • Evolving API • Multiple SCTP implementations • Solution • Integrate SCTP via COTS Middleware • SCTP was added as a Transport Protocol for GIOP messages (SCIOP) • OMG TC Document mars/2003-05-03 • Bound recovery time of CORBA objects after a network failure • SCTP was added as a Transport Protocol to CORBA Audio/Video Streaming Service • Proof of concept: Integration of SCTP in UAV Application • UAV is a reconnaissance image data streaming DRE application

  5. Adaptation Strategies Load balancing • Migrating tasks to less loaded hosts Network management • Diffserv • Reservation Data management • Filtering • Tiling, compression • Scaling CPU management • Scheduling • Reservation Distributed UAV Image Dissemination Mission Requirements • Piloting • Requires an out-of-the-window view of imagery • Surveillance • Must not lose any important imagery • Command/Control • Require high fidelity imagery

  6. CORBA AVStreams Overview • StreamCtrl • controlling the stream • MMDevice • interface for logical or physical device • StreamEndPoint • network specific aspects of a stream • Vdev • properties of the stream

  7. AVStreams Pluggable Protocol Framework • SCTP added as a transport protocol

  8. Experiments

  9. Protocol Analysis and Comparisons • Several different experiments were performed • Paced invocations • Throughput tests • Latency tests • Several different protocols were used • TCP based IIOP • -ORBEndpoint iiop://host:port • UDP based DIOP • -ORBEndpoint diop://host:port • SCTP based SCIOP • -ORBEndpoint sciop://host1+host2:port

  10. Primary Configuration • Both links are up at 100 Mbps • 1st link has 1% packet loss • Systematic link failures • Up 4 seconds, down 2 seconds • One link is always available • Host configuration • RedHat 9 with OpenSS7 SCTP 0.2.19 in kernel (BBN-RH9-SS7-8) • RedHat 9 with LKSCTP 2.6.3-2.1.196 in kernel (BBN-RH9-LKSCTP-3) • Pentium III, 850 MHz, 1 CPU, 512 MB RAM • ACE+TAO+CIAO version 5.4.1+1.4.1+0.4.1 • gcc version 3.2.2

  11. Secondary Configuration • Results as expected: • Roundtrip latency about doubled • Throughput more or less the same • Little effect on paced invocations • SCTP failures on Distributor • Maybe related to 4 network cards • Maybe related to the inability to specify addresses for local endpoints • Sender, Distributor, and Receiver were normal CORBA applications • Similar results were also obtained when AVStreaming was used to transfer data between these components

  12. Modified SCTP Parameters • LKSCTP was less reliable, had higher latency and lower throughput relative to OpenSS7 in almost every test • Also had errors when sending large frames

  13. Paced Invocations • Emulating rate monotonic systems and audio/visual applications • Three protocols: IIOP, DIOP, SCIOP • Frame size was varied from 0 to 64k bytes • DIOP frame size was limited to a maximum of 8k bytes • Invocation Rate was varied from 5 to 100 Hertz • IDL interface • one-way void method(in octets payload) • Experiment measures • Maximum inter-frame delay at the server • Number of frames that were received at the server

  14. Protocol = DIOP, Experiment = Paced InvocationsNetwork = Both links are up • Since network capacity was not exceeded, no DIOP packets were dropped • Cannot measure missed deadlines when using DIOP because the client always succeeds in sending the frame, though the frame may not reach the server

  15. Protocol = DIOP, Experiment = Paced InvocationsNetwork = Both links are up • Very low inter-frame delay • DIOP good choice for reliable links • Also good when low latency is more desirable then reliable delivery • Drawback: Frame size limited to about 8k

  16. Protocol = IIOP, Experiment = Paced InvocationsNetwork = Both links are up • Under normal conditions, no deadlines were missed

  17. Protocol = IIOP, Experiment = Paced InvocationsNetwork = Both links are up • Very low inter-frame delay • IIOP good choice in most normal situations

  18. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = Both links are up • Under normal conditions, very comparable to DIOP and IIOP

  19. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = Both links are up • Under normal conditions, very comparable to DIOP and IIOP

  20. Summary of Experiments under Normal Network Conditions • Under normal conditions, performance of DIOP, IIOP, and SCIOP is quite similar • No disadvantage of using SCIOP under normal conditions

  21. Protocol = DIOP, Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • Packet loss introduced at Traffic Shaping Node causes frames to be dropped • 1% to 7% frames were dropped – higher loss for bigger frames

  22. Protocol = DIOP , Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • Increase in inter-frame delay due to lost frames • Slowest invocation rate has highest inter-frame delay

  23. Protocol = IIOP, Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • Packet loss did not have significant impact on smaller frames or slower invocation rates since there is enough time for the lost packets to be retransmitted • Packet loss did impact larger frames, specially the ones being transmitted at faster rates – 6% of 64k bytes frames at 100 Hz missed their deadlines

  24. Protocol = IIOP, Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • IIOP does not recover well from lost packets • 720 msec delay for some frames (only 13 msec under normal conditions)

  25. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • SCIOP was able to use the redundant link during packet loss on the primary link • No deadlines were missed

  26. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = 1% packet loss on 1st link • Inter-frame delay in this experiment is very comparable to the inter-frame delay under normal conditions (26 msec vs. 14 msec)

  27. Summary of Experiments under 1% packet loss on 1st link • Client was able to meet all of its invocation deadlines when using SCIOP • DIOP dropped up to 7% of frames • IIOP missed up to 6% of deadlines

  28. Protocol = DIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • Link was down for 33% of the time • 33% of frames were dropped

  29. Protocol = DIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • Link was down for 2 seconds • Inter-frame delay was about 2 seconds

  30. Protocol = IIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • Link failure has significant impact on all invocation rates and frame sizes • Impact is less visible for smaller frames at slower rates because IIOP is able to buffer packets thus allowing the client application to make progress • Up to 58% deadlines are missed for larger frames at faster rates

  31. Protocol = IIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • IIOP does not recover well from temporary link loss • Maximum inter-frame delay approaching 4 seconds

  32. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • SCIOP was able to use the redundant link during link failure • No deadlines were missed

  33. Protocol = SCIOP, Experiment = Paced InvocationsNetwork = Systemic link failure • Inter-frame delay never exceeded 40 msec

  34. Summary of Experiments under Systemic link failure • Client was able to meet all of its invocation deadlines when using SCIOP • DIOP dropped up to 33% of frames • IIOP missed up to 58% of deadlines

  35. Throughput Tests • Emulating applications that want to get bulk data from one machine to another as quickly as possible • Two protocols: IIOP, SCIOP • DIOP not included because it is unreliable • Frame size was varied from 1 to 64k bytes • Client was sending data continuously • IDL interface • one-way void method(in octets payload) • void twoway_sync() • Experiment measures • Time required by client to send large amount of data to server

  36. Experiment = ThroughputNetwork = Both links are up • IIOP peaks around 94 Mbps • SCIOP is up to 28% slower for smaller frames • SCIOP is able to utilize both links for a combined throughput up to 122 Mbps

  37. Experiment = ThroughputNetwork = 1% packet loss on 1st link • 1% packet loss causes maximum IIOP bandwidth to reduce to 87 Mbps (8% drop) • IIOP outperforms SCIOP for smaller frames • SCIOP maintains high throughput for larger frames, maxing out at 100 Mbps

  38. Experiment = ThroughputNetwork = Systemic link failure • Link failure causes maximum IIOP throughput to drop to 38 Mbps (60% drop) • SCIOP outperforms IIOP for all frame sizes • SCIOP maxes out at 83 Mbps

  39. Latency Tests • Emulating applications that want to send a message and get a reply as quickly as possible • Two protocols: IIOP, SCIOP • DIOP not included because it is unreliable • Frame size was varied from 0 to 64k bytes • Client sends data and waits for reply • IDL interface • void method(inout octets payload) • Experiment measures • Time required by client to send to and receive a frame from the server

  40. Experiment = LatencyNetwork = Both links are up • Mean IIOP latency comparable to SCIOP • For larger frames, maximum latency for SCIOP is 15 times maximum latency for IIOP

  41. Experiment = LatencyNetwork = 1% packet loss on 1st link • 1% packet loss causes maximum IIOP latency to reach about 1 second • SCIOP outperforms IIOP for both average and maximum latencies for all frame sizes

  42. Experiment = LatencyNetwork = Systemic link failure • Link failure causes maximum IIOP latency to reach about 4 seconds • SCIOP outperforms IIOP for both average and maximum latencies for all frame sizes

  43. ExperimentsSummary

  44. Conclusions • SCTP combines best features of TCP and UDP and adds several new features • SCTP can be used to improve network fault tolerance and improve QoS • Under normal network conditions, SCTP compares well with TCP and UDP • In addition, it can utilize redundant links to provide higher effective throughput • Under packet loss and link failures, SCTP provides automatic failover to redundant links, providing superior latency and bandwidth relative to TCP and UDP • Integrating SCTP as a pluggable protocol into middleware allows effortless and seamless integration for DRE applications • SCTP is available when using ACE, TAO, CIAO and AVStreaming • Continue to use other network QoS mechanisms such as DiffServ and IntServ with SCTP • Both OpenSS7 and (specially) LKSCTP implementations need improvement • Crashes during failover • Differences in conformance to SCTP specification • Limited technical support • Emulab provides an excellent environment for testing SCTP • Future work • Load-sharing in SCTP – Concurrent multipath data transfer • Adaptive Failover • Ongoing research at Protocol Engineering Laboratory, University of Delaware

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